In occasions such as an office conference, multimedia teaching or entertainments, a projector may generally be used for projecting images onto a wall or a projection screen, so as to render a larger picture. In a process of using the projector, it is difficult to arrange a projection direction of the projector perpendicular to the wall and facing a center of the projection screen or the wall. Thus, when the projector emits a projection beam, diffusion of the projection beam reaching a part of the wall nearer to the projector is smaller than that of the projection beam reaching a part of the wall farther to the projector, so that an upper and a lower edges or a left and a right edges of a corresponding projection image have different lengths, which causes deformation on the projection image which is originally a rectangle and a server distortion of the projection image. For example, in FIG. 1 (a), the projector is located under the center of the wall. The diffusion of the projection beam reaching the lower part of the wall is smaller than that of the projection beam reaching the upper part of the wall, and thus the deformation occurs on the projection image, so as to obtain a trapezoid as shown in FIG. 1 (b). Therefore, it is required to calibrate the projection image, in order to display a normal projection image.
During projection, before the projection of the projector, a calibration matrix may be set according to a relative distance between the projector and a projection plane; a whole projection image may be calibrated according to the calibration matrix. When the whole projection image is calibrated according to the calibration matrix, the projection image is deformed according to a form reverse to the formation after the projection, so that the deformation of the calibrated projection image and the deformation after the projection may be cancelled. Then, the calibrated projection image may be projected to the projection plane.
However, the inventor found at least a technical problem in the above techniques as follows during implementation of technical solutions in embodiments of the present disclosure.
When the projection image needs to be projected to a plurality of projection planes, the calibration matrix is set according to the relative distance between the projector and one projection plane, then the whole projection image is calibrated by the calibration matrix. That is, the same calibration matrix is used for the whole projection image, so that the projection image on one of the projection planes may be displayed normally, while the projection images on other projection planes may still deform. Therefore, calibration accuracy of the projection method is not high.